An image forming apparatus generally forms a latent image on a photoconductive drum, develops and visualizes the latent image with toner, and then transfers the visualized toner image to a recording paper and fixes the visualized toner image on the recording paper by heating. Heating is needed on the fixing process, and a fixing device which heats and fixes an image through induction heating is known.
The heating temperature control in the fixing device is important, and in the induction heating, generally, the power supplied for an IH coil is controlled to control the heating temperature. However, if the temperature is set to a given value, the frequency of changing power is increased and the temperature ripple is increased. When the temperature is low, an image defect is caused and a stable fixing processing cannot be carried out due to the low temperature offset and the like. Thus, it is necessary to maintain the heating temperature in a constant width and reduce the temperature ripple.
However, in most cases, the fixing condition changes due to the temperature in the image forming apparatus even if the heating temperature is maintained in a constant width, which leads to an unstable fixation.
Thus, the purpose of the present invention is to provide an image forming apparatus capable of carrying out a stable fixing processing constantly.